[wdmaudiodev] Re: USB Audio specification - feature unit question

  • From: Matthew van Eerde <Matthew.van.Eerde@xxxxxxxxxxxxx>
  • To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Mon, 10 Sep 2012 15:47:35 +0000

Windows will inject a software mute control if the driver does not provide a 
hardware mute control.

If you look at the filter nodes in  KS Studio you can tell whether the driver 
is exposing a hardware mute, or you can call 
IAudioEndpointVolume::QueryHardwareSupport from an app.

From: wdmaudiodev-bounce@xxxxxxxxxxxxx 
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Bartosik Lukasz-ALB045
Sent: Monday, September 10, 2012 6:01 AM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] USB Audio specification - feature unit question


I've got a question related to behavior of feature unit in Windows 7.

I have a feature unit which supports only volume control for master channel:

===>Audio Control Feature Unit Descriptor<===
bLength:                           0x09
bDescriptorType:                   0x24
bDescriptorSubtype:                0x06
bUnitID:                           0x06
bSourceID:                         0x05
bControlSize:                      0x01
iFeature:                          0x00

And when I go to "Levels" tab in properties for that audio device the volume 
slider is there,
however there is also mute control enabled even though configuration of feature 
unit advertised support for volume only.

Any clues why mute control is not disabled ?


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